Process for treating semiconductor fabrication reclaim

ABSTRACT

The hydrophilic organic contaminants and hydrogen peroxide present in semiconductor fabrication reclaims are removed by means of adsorption of a pyrolysate of a macroreticular sulphonated vinyl-aromatic polymer having a carbon content of at least 85% by weight and a carbon/hydrogen atomic ratio of from 1.5:1 to 20:1. In spite of their hydrophobic surface, the pyrolysates have a comparatively high adsorptivity for these contaminants and provide for distinctively higher removal rates than customary activated carbons.

FIELD OF THE INVENTION

The invention relates to a process for removing hydrophilic organiccontaminants from semiconductor fabrication reclaims by means ofadsorption.

BACKGROUND OF THE INVENTION

In the course of the fabrication of integrated circuits (chips) thewafers must, after certain operations, inter alia after etching, berinsed with various chemicals and with highly pure water. The reclaim,produced in large amounts, is of a quality, owing to the content oforganic and inorganic substances, which makes any direct recycling intothe ultra-pure water production circuit impossible. On the other hand,recycling of the reclaim is considerably impeded by the organiccontaminants arising from semiconductor fabrication, since it isnecessary to achieve TOC values (Total Organic Carbon content) of lessthan 5 ppb in the ultra-pure water circuit, and these organiccontaminants can, as a rule, be removed only inadequately by means ofconventional processes such as reverse osmosis, mixed-bed filters,devolatilization, UV irradiation and ultrafiltration.

Typical semiconductor reclaims contain inorganic and organic substancessuch as, for example, fluoride, chloride, nitrate, sulphate, phosphateand ammonium ions, hydrogen peroxide, isopropanol, acetone,N-methylpyrrolidone, tetramethylammonium hydroxide, methanol, ethanol,butanol, acetic acid, dimethyl sulphoxide, propylene glycol methyl etheracetate and the like. The main constituents usually compriseisopropanol, acetone, N-methylpyrrolidone, hydrofluoric acid,hydrochloric acid, sulphuric acid, phosphoric acid, hydrogen peroxide,ammonia, ammonium fluoride, tetramethylammonium hydroxide and the like.The reclaims may typically have an electrical conductivity of from about10 to 2,000 μS/cm and a TOC value of from about 0.1 to 20 ppm. The pH isgenerally between about 2 and 9, usually below 7.

On the grounds of cost and environmental protection and on the groundsof water scarcity it is desirable for these reclaims, whose overallcontaminant content as a rule is distinctly below that of ordinary tapwater, to be treated to the extent of them being usable once more insemiconductor fabrication.

The treatment of the reclaims at present makes use of ion exchangeprocesses, reverse osmosis processes, adsorption on activated carbon,biological processes and ultrafiltration. For example, free mineralacids and organic acids are removed routinely via weakly or stronglybasic anion-exchange resins. Furthermore, reverse osmosis installationswhich, in some cases, are already present in the make-up water treatmentsystems of the ultra-pure water installations are as a rule quite able,together with the existing ion-exchange stages, to remove both inorganicand organic acids, bases and salts to an adequate degree. Hydrogenperoxide and hydrophilic organic compounds such as isopropanol, acetone,N-methylpyrrolidone, methanol, ethanol, butanol, dimethyl sulphoxide andthe like, on the other hand, are usually removed only in amounts ofabout 50-70%, even in reverse osmosis stages, falling far short of thedemanded TOC values of less than 5 ppb. In principle, it is possible forthe concentrations of these compounds to be further reduced byadditional treatment with activated carbon, but even in this manner itis often impossible or at least extremely difficult to achievesatisfactory separation.

The known processes therefore have the drawback that a number ofpurification methods have to be combined and that nevertheless,particularly in the case of comparatively high concentrations of organiccontaminants, satisfactory results often cannot be achieved, and/orbiofouling may adversely affect the stages downstream of a biologicalstage or an activated-carbon filter.

On the other hand, U.S. Pat. No. 4,040,990, JP-A-62/197308, U.S. Pat.No. 4,839,331, EP-A-0604110 and EP-A-0623557, for example, disclosecarbonaceous adsorbents which are obtained by pyrolysis of syntheticpolymers and, compared with activated carbon, have a more hydrophobicsurface and are therefore able to adsorb hydrophobic organic compounds,in particular hydrocarbons and halogenated hydrocarbons, moreeffectively than activated carbon. Such products are commerciallyavailable, e.g., under the brand name Ambersorb (Rohm and Haas,Philadelphia, USA).

EP-A-0285321 further proposed the use of pyrolysates of cross-linkedpolymers as adsorbents to remove bacterial endotoxins(lipopolysaccharides), which may be present as pyrogens in tap water orin purified water, e.g. as a result of storage. Suitable cross-linkedpolymers are, for example, styrene-divinylbenzene copolymers which, ifrequired, may have been sulphonated or chloromethylated and thenaminated to give an ion-exchange resin. As EP-A-285321 furtherdiscloses, this method can also be used in water treatment processes inwhich highly pure water is produced and stored, by means of the storedwater, prior to a subsequent filtration step, being brought into contactwith the pyrolysate. In this case, however, the starting material forproducing ultra-pure water is tap water, and the adsorption step servesonly for the removal of any pyrogens present from the stored highly purewater.

SUMMARY OF THE INVENTION

Surprisingly we have now found that pyrolysates of macroreticularsulphonated vinyl-aromatic polymers are capable of distinctly moreeffective adsorption of the hydrophilic organic contaminants andhydrogen peroxide present in semiconductor fabrication reclaims than isactivated carbon, in spite of the more hydrophobic surface of theformer. Moreover, it has been found that the contaminants adsorbed onthe said pyrolysates are significantly more readily desorbable thanthose adsorbed on activated carbon.

The invention therefore relates to a process for removing hydrophilicorganic contaminants which are miscible with water at 15° C. in amountsof at least 10% by weight and/or of hydrogen peroxide from semiconductorfabrication reclaims by means of adsorption, which is characterized inthat the reclaim is passed through a bed of a pyrolysate of amacroreticular sulphonated vinyl-aromatic polymer having a carboncontent of at least 85% by weight and a carbon/hydrogen atomic ratio offrom 1.5:1 to 20:1.

It was found that the process according to the invention results notonly in considerably better removal rates being achieved, but that alsothe adsorption capacity of the pyrolysate is usually significantlyhigher than that of a customary activated carbon. Even with a singleadsorption stage having, e.g., a column height (layer height of the bed)of 60 cm, removal rates of far beyond 90% are achieved, as a rule, whichis especially surprising since, inter alia, good adsorptivity ofhydrophobic pyrolysates for hydrophilic compounds could not have beenexpected and the contaminants in the reclaims are present only inamounts of a few ppm. It is therefore possible, by means of the processaccording to the invention, if necessary by connecting two or moreadsorption stages in series and/or preferably by means of a combinationwith the pre-existing make-up water treatment processes, to readilyachieve the demanded TOC values of less than 5 ppb. Moreover, thepyrolysates which can be used according to the invention have theadvantage, compared with activated carbon which is usually notregenerated, that they can easily be regenerated.

FIG. 1 is a graph showing total organic carbon removal rates, as apercentage of adsorption based on TOC values in feed streams, versus bedvolumes of supplied water.

BRIEF DESCRIPTION OF THE DRAWING

The expression "hydrophilic organic contaminant", within the scope ofthe present invention, refers to non-ionic organic compounds which maybe present in semiconductor fabrication reclaims and are miscible withwater at 15° C. in amounts of at least 10% by weight, in particular tonon-ionic organic compounds which are liquid at 20° C., such as thesolvents, employed in semiconductor fabrication, isopropanol, acetone,N-methylpyrrolidone, methanol, ethanol, butanol, acetic acid, dimethylsulphoxide and propylene glycol ether acetate, in particularisopropanol, acetone and N-methylpyrrolidone.

The expression "vinyl-aromatic polymer", in the scope of the presentinvention, refers to polymers obtained by polymerization of avinyl-aromatic monomer.

The expression "macroreticular" should be interpreted, within the scopeof the present invention, in terms of the polymers in question to agreat extent having pores with a pore radius of at least 25 nm.

The pyrolysates which can be used according to the invention expedientlyhave a carbon content of at least 85% by weight and a carbon/hydrogenatomic ratio of from 1.5:1 to 20:1, preferably from 2:1 to 10:1. Theycan be prepared in a known manner, e.g. in accordance with the methodsdescribed in U.S. Pat. No. 4,040,990, U.S. Pat. No. 4,839,331 andJP-A-62/197308, by controlled thermal degradation from macroreticularsulphonated vinyl-aromatic polymers.

Suitable starting polymers are both homopolymers and copolymers ofmonoethylenically unsaturated monomers such as styrene, vinyltoluene,ethylvinylbenzene, vinylxylene and vinylpyridine, and polyethylenicallyunsaturated monomers such as divinylbenzene, trivinylbenzene,divinyltoluene and divinylpyridine. Generally, however, preference isgiven to copolymers from a monoethylenically and a polyethylenicallyunsaturated polymer. Particular preference is given tostyrene-divinylbenzene copolymers, in particular those which wereobtained by polymerization of 75-90 parts by weight of styrene with25-10 parts by weight of divinylbenzene.

The polymerization can be carried out in accordance with known methods,for example as described in U.S. Pat. No. 4,040,990 and U.S. Pat. No.4,839,331. A preferred method is the suspension polymerization disclosedin U.S. Pat. No. 4,224,415.

The sulphonation of the polymers can likewise be carried out in a knownmanner, for example by means of concentrated sulphuric acid, oleum,sulphur trioxide or chlorosulphonic acid at elevated temperature.Suitable conditions are known, e.g., from U.S. Pat. No. 2,366,007, U.S.Pat. No. 2,500,149, U.S. Pat. No. 4,224,415 and U.S. Pat. No. 4,839,331.

The pyrolysis of the sulphonated polymers can be carried out, asdisclosed e.g. by U.S. Pat. No. 4,040,990 and U.S. Pat. No. 4,839,331,by heating the polymers to a temperature of about 300-1200° C.,preferably about 400-800° C., in an inert gas atmosphere (e.g. nitrogen,helium, neon and/or argon) for about 0.3 to 2 hours. If desired, theinert gas may be admixed with an activating gas such as carbon dioxide,oxygen or water vapour, or an after-treatment by heating to about300-1200° C. in an activating gas can be performed. Pyrolysates whichwere not treated with an activating gas, however, generally exhibitbetter adsorptivity for hydrophilic organic contaminants.

In the course of the pyrolysis of the polymers micropores are formed inaddition to the pores present in the polymer, which are largely retainedduring the pyrolysis. In accordance with the pore size definition byIUPAC a distinction can be made, in the pyrolysate, between macroporeshaving a pore radius of more than 25 nm, mesopores having a pore radiusof from 1 to 25 nm, and micropores having a pore radius of less than 1nm, the adsorption presumably taking place largely in the micropores,while the mesopores and macropores facilitate transport to themicropores.

In the adsorption process according to the invention preference is givento the use of those pyrolysates which have macropores having a specificpore volume of at least about 0.1 ml/g, in particular at least about0.13 ml/g (e.g. 0.20-0.25 ml/g), and mesopores having a specific porevolume of at least about 0.1 ml/g, in particular at least about 0.12ml/g (e.g. 0.13-0.20 ml/g). Furthermore, as a rule preference is givento pyrolysates which have micropores having a specific pore volume of atleast about 0.1 ml/g, particularly preferably at least about 0.2 ml/g(e.g. 0.2-0.4 ml/g). The pore volumes stated in each case correspond tothe values obtained on a Micromeritics 2400 porosimeter from thenitrogen adsorption isotherms. The pore volumes stated are not critical,however, and pyrolysates having smaller pore volumes are in principlealso suitable.

We have further found, surprisingly, that the adsorptivity of thecomparatively hydrophobic pyrolysates for the hydrophilic organiccontaminants present in semiconductor fabrication reclaims evidentlyincreases still further as the hydrophobicity of the pyrolysate surfaceincreases. The fact is that pyrolysates which, at room temperature (24°C.) and a relative humidity of 94%, are able to adsorb less than 300 mgof water per g of pyrolysate, proved particularly suitable, in theprocess according to the invention, for the adsorption of hydrophilicorganic contaminants, the best results being achieved with thosepyrolysates which are able to adsorb less than 200 mg of water per g ofpyrolysate. Regarding the adsorption of hydrogen peroxide, on the otherhand, the comparatively less hydrophobic pyrolysates tend to be moresuitable, observations showing that pyrolysates which, at roomtemperature (24° C.) and a relative humidity of 94%, are able to adsorbat least 200 mg, for example 200-400 mg and preferably 200-300 mg ofwater per g of pyrolysate are more suitable, as a rule, than those whichare able to adsorb less than 200 mg of water per g of pyrolysate.

To remove hydrophilic organic contaminants and hydrogen peroxide it istherefore possible, preferably, to employ two pyrolysates of which oneis able to adsorb at least 200 mg of water and the other less than 200mg of water per g of pyrolysate. The process can be implemented in sucha way that the reclaim is passed either through a bed of a mixture ofthe two pyrolysates or successively, in any order, through one bed eachof these pyrolysates.

The pyrolysates are highly stable, chemically, thermally and physically.In general they have a specific area of about 100-2000 m² /g, usuallyabout 500-1200 m² /g and can be used, for example, in the form ofapproximately spherical particles having a mean particle size of, forexample, from about 0.2 to 1.5 mm, preferably from about 0.3 to 1.0 mm.Suitable pyrolysates are commercially available, e.g., under thedesignations Ambersorb 348F, Ambersorb 572, Ambersorb 575, Ambersorb 563and Ambersorb 564 (Rohm and Haas, Philadelphia, USA), all of them beingsuitable for the adsorption of hydrophilic organic contaminants and ofhydrogen peroxide. Preferably, however, Ambersorb 563 and/or 564 can beused for the adsorption of hydrophilic organic contaminants, andAmbersorb 572 and/or 575 can be used for the adsorption of hydrogenperoxide.

The process according to the invention can be implemented in accordancewith the conventional methods for adsorption processes, the pyrolysatebed preferably being arranged in an adsorption filter or a column whichcan be operated in an up flow process or a down flow process. Generally,a bed height of at least about 30 cm, for example about 60-150 cm is tobe recommended. To improve the removal rate, it is in principle possibleto increase the bed height; in this case, however, it is generally moreadvantageous for two or more pyrolysate beds to be connected in series.Downstream of the pyrolysate bed there may preferably be a weakly basicanion exchanger.

If fresh pyrolysates are used it is advisable for deionized water to bepassed through the pyrolysate bed for a few days prior to start-up, tohydrate the pyrolysate. This preferably involves hot water being passedthrough the bed at first, the further treatment being carried out atroom temperature.

When the pyrolysate is spent or the removal rate drops below a certainvalue, e.g. below 90%, the reclaim supply can be interrupted and thepyrolysate can be regenerated, in a cocurrent or countercurrent process,and be reused. The regeneration can preferably be effected by steamhaving a temperature of from about 100 to 250° C. being passed throughthe pyrolysate. Generally, fewer than about 12 bed volumes of steam(measured as condensate) are sufficient to substantially remove theadsorbed contaminants.

The flow rates may, for example, during operation be about 5-40 bedvolumes of reclaim per hour and during regeneration be about 0.1-2.0 bedvolumes of steam (measured as condensate) per hour.

To avoid any interruption of the reclaim treatment during theregeneration it is possible to provide, preferably, two or threepyrolysate beds, one or two of which are in service at any given time,while one bed is being regenerated.

The adsorption process according to the invention is illustrated in moredetail by the following example.

EXAMPLE 1

Four columns of transparent poly(vinyl chloride) having a columndiameter of 40 cm and a column height of 1.5 m were charged, up to a bedheight of 60 cm (bed volume BV=0.75 l) with one adsorbent each, i.e. forcomparative purposes (A) Amberlite XAD 16 (Rohm and Haas) and (B) theactivated carbon BD (Chemviron) and, according to the invention, (C)Ambersorb 572 (Rohm and Haas) and (D) Ambersorb 563 (Rohm and Haas). Forthe purpose of hydration in the column, the fresh adsorbents haddeionized water flowing through them for 7 days at a flow rate of 1 l/h.Subsequently, in each case during the day, water containing about 10-20ppm of hydrogen peroxide and having a TOC content of 5.2-6.5 ppm,comprising acetone and isopropanol in a weight ratio of 1:1, was passedthrough the columns at a temperature of 20-22° C. and at a flow rate of5 BV/h, and the TOC value and the hydrogen peroxide content in the waterflowing out were measured. Overnight the water supply was interrupted ineach case. The TOC values in the feed stream and the experimentaladsorption capacities until the removal rates dropped to 90% are givenin Table 1, together with the removal rates in % for hydrogen peroxide(decrease of H₂ O₂ in %) . The TOC removal rates as % of adsorptionbased on the TOC values in the feed stream are plotted in FIG. 1 againstthe bed volumes of supplied water. As the results show, distinctlyhigher TOC removal rates are achieved with the pyrolysates usedaccording to the invention, which also have higher adsorptioncapacities.

                  TABLE 1                                                         ______________________________________                                                               Adsorption                                                          ppm of TOC                                                                              capacity in g                                                       in the feed                                                                             of TOC/l of                                            Adsorbent    stream    pyrolysate Decrease H.sub.2 O.sub.2                    ______________________________________                                        (A) Amberlite XAD 16                                                                       5.2       0.03       5-10%                                       (B) Carbon BD                                                                              6.5       0.08       100%                                        (C) Ambersorb 572                                                                          6.1       0.26       100%                                        (D) Ambersorb 563                                                                          5.2       1.93        40%                                        ______________________________________                                    

What is claimed is:
 1. Process for removing hydrophilic contaminantsselected from the group consisting of hydrogen peroxide and hydrophilicorganic contaminants which are miscible with water at 15° C. in amountsof at least 10% by weight from a semiconductor fabrication reclaim bymeans of adsorption, comprising the step of passing the reclaim througha bed of a pyrolysate of a macroreticular sulphonated vinyl-aromaticpolymer having a carbon content of at least 85% by weight and acarbon/hydrogen atomic ratio in a range of from 1.5:1 to 20:1. 2.Process according to claim 1, wherein the pyrolysate has macroporeshaving a pore radius of more than 25 nm and a specific pore volume of atleast 0.1 ml/g and mesopores having a pore radius of from 1 to 25 nm anda specific pore volume of at least 0.1 ml/g.
 3. Process according toclaim 1, wherein the pyrolysate has macropores having a pore radius ofmore than 25 nm and a specific pore volume of at least 0.13 ml/g andmesopores having a pore radius of from 1 to 25 nm and a specific porevolume of at least 0.12 ml/g.
 4. Process according to claims 1 or 2,wherein the pyrolysate has micropores having a pore radius of less than1 nm and a specific pore volume of at least 0.1 ml/g.
 5. Processaccording to claims 1 or 3, wherein the pyrolysate has micropores havinga pore radius of less than 1 nm and a specific pore volume of at least0.2 ml/g.
 6. Process according to any one of claims 1 to 3, wherein thepyrolysate has a carbon/hydrogen atomic ratio in a range of from 2:1 to10:1.
 7. Process according to any one of claims 1 to 3, wherein thepyrolysate is able to adsorb, from air at room temperature and arelative humidity of 94%, less than 300 mg of water per g of pyrolysate.8. Process according to any one of claims 1 to 3, wherein thehydrophilic contaminant to be removed is a hydrophilic organiccontaminant miscible with water at 15° C. in amounts of at least 10% byweight, and wherein the pyrolysate is able to adsorb, from air at roomtemperature and a relative humidity of 94 %, less than 200 mg of waterper g of pyrolysate.
 9. Process according to any one of claims 1 to 3,wherein the hydrophilic contaminant to be removed is hydrogen peroxide,and wherein the pyrolysate is able to adsorb, from air at roomtemperature and a relative humidity of 94%, at least 200 mg of water perg of pyrolysate.
 10. Process according to any one of claims 1 to 3,wherein the pyrolysate is a styrene-divinylbenzene copolymer. 11.Process according to any one of claims 1 to 3, wherein the pyrolysate isa styrene-divinylbenzene copolymer having a weight ratiostyrene/divinylbenzene in a range of from 75:25 to 90:10.
 12. Processaccording to any one of claims 1 to 3, wherein the pyrolysate has a meanparticle size of from 0.2 to 1.5 mm.
 13. Process according to any one ofclaims 1 to 3, further comprising the steps of interrupting the flow ofthe reclaim through the pyrolysate bed and then passing steam having atemperature of from 100 to 250° C. through the pyrolysate bed. 14.Process according to claim 1, wherein the reclaim initially has a totalorganic carbon content (TOC) in the range of about 0.1 to 20 ppm and theprocess lowers the TOC to less than about 5 ppb.
 15. Process fordecontaminating aqueous semiconductor reclaim, comprising:removinghydrophilic organic contaminants which are miscible with water at 15° C.in amounts of at least 10% by weight and/or hydrogen peroxide by meansof adsorption, said adsorption including passing said reclaim through abed of pyrolysate of a macroreticular sulphonated vinyl-aromatic polymerhaving a carbon content of at least 85% by weight and a carbon/hydrogenatomic ratio of from 1.5:1 to 20:1.
 16. Process according to claim 15,wherein the reclaim initially has a total organic carbon content (TOC)in the range of about 0.1 to 20 ppm and the process lowers the TOC toless than about 5 ppb.